WASHINGTON (AP) - Congress' top Democrat accused Republicans on Friday of risking a government shutdown because they want to make it harder "for women to get cancer screenings."

Senate Majority Leader Harry Reid unleashed his attack as his main antagonist in long-running negotiations, Speaker John Boehner, said spending cuts _not social issues -- was blocking agreement to prevent a shutdown at midnight.

The maneuvering unfolded as President Barack Obama canceled a trip to Indianapolis and spoke in separate phone calls with Reid and Boehner.

"Discussions between the leaders and the White House aimed at reaching a budget agreement are continuing," White House press secretary Jay Carney said in a written statement.

Obama, Reid and Boehner met at the White House on Thursday evening for the third time in two days, and their aides struggled without success to reach agreement in middle-of-the-night talks in the Capitol.

Republicans have been seeking $40 billion in cuts, as well as several other provisions to advance the conservative agenda backed by a rank and file that includes dozens of first-termers elected with the support of tea party activists.

As the Senate opened for business, Reid said the two sides had reached agreement on $38 billion in spending cuts and the only hangup was a Republican demand to cut a federal program that provides women's health and family planning services.

"They are willing to throw women under the bus, even if it means they'll shut down the government," he said.

"Republican leaders in the House have only a few hours left to look in the mirror, snap out of it and realize how positively shameful that would be."

But Boehner said the two sides were "close to a resolution" on the non-spending issues, and there was "only one reason that we do not have an agreement as yet, and that issue is spending."

"When will the White House and when will Senate Democrats get serious about cutting federal spending?" he asked rhetorically.

Boehner urged Obama to reconsider a veto threat against legislation to keep the government open for one additional week while negotiators continue working on a deal to fund federal programs through Sept. 30.

That measure includes $12 billion in spending cuts, and provides enough funds to keep the Pentagon in operation through Sept. 30.

Barring an agreement or perhaps another temporary bill to keep the government operating, the shutdown of most of the government would begin at midnight. Many essential workers, such as mail carriers, air traffic controllers and the military, would stay on the job.

Obama said ominously on Friday night that the machinery of a shutdown was already in motion.